The present application claims priority to Japanese Application No. P2000-229731 filed Jul. 28, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to an exposure method for super-fine processing in the semiconductor field, for example.
2. Description of the Related Art
In the semiconductor field, for example, there is a need to establish a novel process technique enabling super-fine pattern processing of 0.1 xcexcm or below, for example.
For fine pattern processing, the so-called lithography technique is indispensable. That is, a photosensitive resist layer is formed on a substrate and the resist layer is exposed to light for patterning. In order to reduce the exposure light wave length to improve the optical resolution for super-fine processing, conventionally, g-rays or i-rays of mercury lamps and ultraviolet rays of excimer laser of KrF (krypton fluorine: wavelength 248 nm) and ArF (argon fluorine: wavelength 193 nm) have been used industrially. These techniques have been used for elements of design rule 0.13 xcexcm or above because of the restriction of the resolution by the wavelength.
On the other hand, there is an urgent necessity to develop a novel lithography technique capable of preparing elements of design rule 0.1 xcexcm or below. For this, a novel lithography technique using vacuum ultraviolet (VUV) rays of wavelength 170 nm or below has been vigorously developed for further reducing the exposure light source wavelength which has been used in the conventional lithography technique.
More specifically, a lithography technique using F2 (fluorine dimer) excimer laser having a wavelength of 157 nm has been developed to replace the conventional ArF lithography. Furthermore, a lithography technique using Ar2 (argon dimer) excimer laser having a wavelength of 126 nm has been suggested to replace the F2 lithography technique.
By the way, the polymer material constituting the conventional resist layer has an aromatic cycle or an alicyclic group for maintaining the etching resistance. For example, the novolac resin which is a resin for the i-ray lithography and the polyhydroxystyrene resin which is a resin for the KrF lithography both has aromatic cycles. However, the aromatic cycles have a great absorption of 193 nm which is the exposure wavelength of the ArF lithography. For this, the acrylic resin for the ArF lithography has an alicyclic group instead of the aromatic cycle.
However, in the region of the vacuum ultraviolet rays, the aromatic cycle and alicyclic groups have a large optical absorption and accordingly, the polymer material constituting the conventional resist layer containing the aromatic cycle or alicyclic group also shows a large optical absorption. For this, in the conventional resist layer, light used cannot reach the bottom of the resist layer, disabling to prepare a resist pattern having a preferable rectangular shape. Thus, the resist patter is deteriorated.
The deterioration of the resist pattern is a great hindrance for super-fine processing and its improvement is desired. In order to work around this problem, for example, the film thickness of the resist layer is reduced to 70 nm or less, thereby improving the light transmittance in the entire resist layer. However, when the resist layer film thickness is reduced, the arises a problem that the etching resistance becomes insufficient. Furthermore, when the resist layer film thickness is reduced, there also arises a problem that the number of defects in the resist layer is increased.
For these reasons, a study has been made to apply a surface imaging method using a silylation reaction and capable of patterning even when the light transmittance is low. However, when the surface imaging method is applied, there is a problem that an edge portion of the resist pattern is remarkably rough. Furthermore, when the surface imaging method is applied, there is a problem that the dimension control is insufficient.
It is therefore an object of the present invention to provide an exposure method enabling a super-fine processing by solving the problem of the light transmittance of a resist layer in the region of the vacuum ultraviolet ray wavelength.
In order to achieve the aforementioned object, the present invention provides an exposure method for exposing a resist layer with vacuum ultraviolet rays for patterning into a predetermined shape, wherein a polymer material constituting the resist layer is a polymer material having at least one alicycle which is a saturated n-member ring (n is a number of carbon atoms constituting the ring and is an even number) and a fluorine substitution group in at least two carbon atoms constituting the alicycle and arranged alternately.
Normally, the alicyclic groups have a large absorption in the vacuum ultraviolet ray region and accordingly, the polymer material constituting a resist layer for VUV (vacuum ultraviolet) lithography cannot contain alicyclic groups.
On the other hand, it is known that when the hydrogen atom contained in the alicyclic group is substituted by a fluorine atom, the alicyclic group having the fluorine substitution group has a reduced optical absorption as compared to the one not containing the fluorine substitution group. When considering only lowering the absorption in the vacuum ultraviolet ray region, it is most preferable to substitute all the hydrogen atoms contained in the alicyclic group with fluorine atoms.
However, a polymer material containing a perfluorized alicyclic group tends to remarkably lower the adhesion with a silicon oxide film as the undercoat of the resist film or with an organic or inorganic antireflection film. Moreover, this polymer material has a tendency that as the substitution ratio of the contained hydrogen atoms with fluorine atoms is increased, the etching resistance is deteriorated.
According to the present invention, by substituting particular hydrogen atoms contained in a particular alicycle with fluorine atoms, it is possible to suppress deterioration of the adhesion and the etching resistance as well as to suppress optical absorption of the entire polymer material in the vacuum ultraviolet ray region.